The invention relates to a device for altering the control times of gas exchange valves of an internal combustion engine, especially an apparatus for hydraulic rotational angle adjustment of a camshaft relative to a crankshaft, in which the device is arranged on the drive side end of a camshaft mounted in the cylinder head of the internal combustion engine and is basically constructed as hydraulic actuator controllable as a finction of various operating parameters of the internal combustion engine. The device includes a drive unit drivingly connected with a crankshaft and bounded axially by two lateral covers as well as of an output unit connected in a rotationally fast manner to a camshaft and inserted into the drive unit. The drive unit of the device is connected to provide power transmission to the output unit of the device through at least two pressure chambers formed inside the device, which are alternatively or simultaneously acted upon by a hydraulic pressure medium, The action of pressure in the pressure chambers takes place under constant compensation for external pressure medium leakages and brings about a relative twisting or a hydraulic clamping of the output unit in relation to the drive unit. For adapting the adjustment speed of the device in both adjustment directions as well as for attaining a preferred position of the output unit toward the drive unit for the start of the internal combustion engine, the device has a spring apparatus constructed as a coil spring arranged outside the device in front of a lateral cover of the drive unit which is fastened with one end on the drive unit and with the other end on the output unit, and it is especially advantageously realizable on an apparatus for hydraulic rotational angle adjustment of a camshaft relative to a crankshaft.
From DE 100 01 200 A1, a representative device for altering the control times of the gas exchange valves of an internal combustion engine is known which is arranged on the drive-side end of a camshaft mounted in the cylinder head of an internal combustion engine and is constructed, depending upon various operating parameters of the internal combustion engine, of controllable hydraulic actuators. This device basically includes a drive unit drivingly connection with the crankshaft and axially bounded by two walls, as well as an output unit connected in a rotationally fixed manner with the camshaft and inserted into the drive unit, which stand in power transmitting connection through at least two pressure chambers pressure chambers constructed within the device which are alternatively or simultaneously subject to action by a hydraulic pressure medium. The drive unit is formed in connection with this device by a hollow cylinder drive gear constructed with exterior teeth in which, due to radial partitions, several hydraulic operating spaces arise. Correspondingly, with this device, an impeller is provided as output unit which is constructed with several vanes extending radially away from its wheel hub which subdivide the operating spaces in the drive unit into at all times two of the hydraulic pressure chambers mentioned. When these pressure chambers are acted upon by pressure, there consequently arises (with constant compensation for external pressure medium leakage) a relative rotation or a hydraulic clamping of the output unit of the device, and therewith of the camshaft in relation to the crankshaft of the internal combustion engine. In addition, this device has, for adapting their adjustment speeds in both adjustment directions as well as for reaching a preferred position of the output unit in relation to the drive unit for starting the engine, a spring apparatus which is constructed as a coil spring arranged outside the device adjacent to a side cover of the drive unit and fastened with one end on the drive unit and with the other end on the output unit.
With this known device, it has nonetheless turned out in practice that the coil spring used is excited to sympathetic vibrations on the basis of its free arrangement outside the device by the vibrations emitted by the internal combustion engine. If the coil spring then oscillates in its resonant frequencies, in an unfavorable case oscillation amplitudes of such magnitude occur that the excess tension elevations lead to breakage of the coil spring. With an altered winding of the coil spring, the resonance frequency can indeed be diminished by restricting the path of the spring turn available for oscillation. But such measures have not proved sufficient for designing the coils springs secure against breakage.
For this reason, the object is to provide a device for altering the control times of gas exchange valves of an internal combustion engine, especially an apparatus for hydraulic rotational angle adjustment of a camshaft in relation to a crankshaft, where without impairing the function of the device as well as without alterations of the structural space of the device, using simple means, an oscillation of the coil spring excited by vibrations of the internal combustion engine in its resonant frequencies, and an oscillation breakage of the coil spring therewith, is avoided.
This object is accomplished with a device according to the invention in such a way that the coil spring arranged outside the device is arranged using an additional housing in a closed annular space formed together with the adjacent side cover of the drive unit through encapsulation, which in interaction with the centrifugal forces arising in the operation of the internal combustion engine, is completely fillable with the external pressure medium leakage from the device, and out of which the hydraulic pressure medium is once again dissipatable as leakage, whereby when the annular space is completely filled, the hydraulic pressure medium functions at the same time as a damping agent against the resonant frequencies of the spring turns of the coil spring resulting from vibrations of the internal combustion engine.
In a preferred aspect of the device constructed in accordance with the invention, the additional housing is made of a cup-like housing cover into the base of which a coaxial circular opening is provided, which forms the outer bounding walls of the annular space, as well as well as of a casing-like housing hub which is insertable into the circular opening in the housing cover and which forms the internal boundary wall of the annular space. The two part construction of the additional housing has proven to be particularly advantageous with respect to the economical manufacture of the housing parts as stamped-drawn parts as well as with respect to fastening the ends of the coil spring on the one hand on the drive unit and on the other on the output unit. Nevertheless, a more than two part construction of the housing is also possible, along with its manufacture in non-cutting formed or a machined part.
An further advantageous configuration of the cup-like housing cover of the device constructed in accordance with the invention includes a circumferential wall which has an inner diameter corresponding approximately to the outer diameter of the adjacent side cover of the drive unit as well as a lengthened edge part with which the housing cover is affixable on the side cover of the drive unit. The circumferential wall is here preferably bent at right angles to the base of the housing cover and, due to the lengthened edge part, has a height which goes slightly beyond the width of the coil spring arranged in the annular space.
For affixing the housing cover on the lateral cover of the drive unit, the housing cover has in further configuration of the invention a circular step in its circumferential wall which lies face-side on the lateral cover of the drive unit and consequently on the one hand forms an axial stop for the housing cover to avoid an axial clamping of the coil spring arranged on the housing, and on the other hand centers the housing cover toward the lateral cover of the drive unit. Through several detents distributed uniformly in the circumference in the extended edge part of the circumferential wall of the housing cover which extend behind the lateral cover of the drive unit, the housing cover is then fastened form-locking on the lateral cover of the drive unit as well as secured axially against unintentional separation. The free space necessary for the detents can then be created either through a circular perforation into the adjacent edge part of the housing surface of the drive unit or through a lateral cover of the drive unit slightly larger in diameter than the drive unit. As an alternative to this, it is also possible to work only local depressions into the edge part of the housing surface of the drive unit which are arranged at the same distance as the detents on the housing cover toward one another and have at least their breadth so that the housing cover is additionally protected against torsion. To avoid pressure medium leakages at this connection point, it has moreover proven advantageous to place between the step in the circumferential wall of the housing cover and the lateral cover of the drive unit an annular seal of rubber or plastic which (in connection with fastening the housing cover over the detents in its circumferential wall) is axially braced between the housing cover and the drive unit. Alternatively, the attachment of the housing cover on the lateral cover of the drive unit can be a press fit, and consequently seal off the connection point between the housing and the lateral cover without additional sealant radially against pressure medium leakages.
The casing-like housing hub of the device constructed according to the invention has, in an advantageous configuration, a cylinder wall with an outer diameter approximately corresponding to the inner diameter of the circular opening in the housing cover which is constructed for retaining the housing hub on the drive unit on its face with a bend directed inwardly. In this way, an annular base is formed on the housing hub through which a central screw installed into the housing hub can be passed, with which the housing hub together with the output unit of the device is screwed on the camshaft. In its axial length, the housing hub is constructed such that it projects with its other face slightly out of the circular opening in the housing cover and closes this off toward the outside through a bend in its edge part. Since the housing hub, through its fastening on the output unit, is connected fast with the camshaft, this edge part projecting out of the housing cover can be used especially advantageously for fastening further components necessary for the finction of the device, for example through connection with an impulse-generating disk of an apparatus for ascertaining the camshaft position in relation to the crankshaft position or the like.
A further feature of the casing-like housing hub of the device constructed according to the invention is that its cylinder wall is partially constructed as a hollow square on which the complementarily constructed inner end of the coil spring is fastened form-locking. This especially concerns the part of the cylinder wall arranged inside the annular space of the housing and means that the inner end of the coil spring is preferably shaped such that it surrounds at least three sides of the hollow square of the housing hub and consequently arrests the coil spring through a form locking torsion-resistant connection to the housing hub as well as through this once again toward the output unit of the device. The diameter of the hollow cylindrical part of the housing hub and the lateral length of the hollow square of the housing hub are here preferably constructed identically and correspond approximately to the diameter of the screw head of the central screw with which the housing hub and the output unit are screwed on the camshaft. It is also possible to provide the diameter of the housing hub and the lateral length of the hollow square with different dimensions, or to provide the housing hub with another polygonal hollow section cross section on which the inner end of the coil spring then is in any given case complementarily adapted for form-locking fastening on the housing hub. Likewise, the housing hub can be constructed as a hollow cylinder over its entire length, and be fastened to the inner end of the coil spring constructed in this case without additional deflections through a rivet or screw connection or the like force-locking on the housing hub.
The outer end of the coil spring is, in a further configuration of the device constructed in accordance with the invention, preferably constructed with a bent hook-like shape and attached form-locking on a point of suspension projecting axially away on the drive unit of the device. It has proven especially advantageous to construct this point of suspension for the outer end of the coil spring through a component arranged in any case on the drive unit of the device, as for example, with rotation piston adjusters through an extended fastening screw on the lateral cover of the drive unit, whereby nonetheless points of suspension can also be arranged on the drive Unit especially for the spring attachment. Likewise, it is also possible here to construct the outer end of the coil without additional deflections, and to fasten it through a rivet or screw connection of the like force-locking on the drive unit of the device.
Finally, as a further feature of the device constructed in accordance with the invention, the external pressure medium leakages of the device are selectively discharged through slot seals between the drive unit and the output unit to a coaxial opening in the side cover of the drive unit adjacent to the housing and are from there introduced into the annular space of the housing through an annular slot between the opening in the lateral cover and the exterior of the housing hub. These external pressure medium leakages occur due to construction in all known hydraulic devices for rotational angle adjustment of a camshaft, whereby the volume and pressure loss associated therewith in the hydraulic pressure spaces of the device are permanently compensated by a corresponding control unit of the device. In this way, there occurs in operating the internal combustion engine a continual leakage flow which is diverted, at least in chain or gear driven devices, usually directly into the cylinder head of the internal combustion engine, but with the device constructed in accordance with the invention is at least caught in the additional housing. The pressure medium leakages caught are here completely pressureless and flow on the path described into the housing until the annular space formed in this is completely filled, and the spring turns of the coil spring are enclosed by the pressure mediums on all sides. The pressure medium situated between the spring windings must consequently be permanently displaced when the spring rises, and through its viscosity brings about a damping of spring vibrations. Through an additional annular slot between the housing cover and the housing hub, the pressure medium leakages are then diverted in a known manner out of the housing again into the cylinder head of the internal combustion engine, whereby it is alternatively also possible to conduct the supply and/or discharge of the pressure medium leakages into and out of the housing through inlets and outlets independently provided for this.
The device constructed in accordance with the invention for altering the control times of gas exchange valves of an internal combustion engine, especially an apparatus for hydraulic rotational angle adjustment of a camshaft relative to a crankshaft, consequently has the advantage in relation to the devices known from the state of the art that the coil spring arranged outside the device in front of one of the lateral covers on the drive unit by means of encapsulation through an additional housing, which is fillable with the pressure medium leakages present in any case, is now no longer arranged free, but rather is enclosed on all sides by the hydraulic pressure medium of the device, and consequently is hydraulically dampened in its sympathetic vibrations excited on the basis of vibrations from the internal combustion engine. In this way, the oscillation amplitudes are reliably kept so low that no excess tensions occur in the spring turns, and in any case, a vibration breakage of the coil springs is avoided. Moreover, a damping of this type has proven to be durable and in addition has the advantage that the function of the device is not influenced and that the additional housing requires no changes in the space available for the device.